The present invention relates to a method of controlling an internal combustion engine including a variable speed fan.
In the control of heavy duty internal combustion engines, the conventional practice utilizes electronic control units having volatile and non-volatile memory, input and output driver circuitry, and a processor that executes instructions to control the engine and its various systems and sub-systems. A particular electronic control unit communicates with numerous sensors, actuators, and other electronic control units to control various functions, which may include various aspects of field delivery, transmission control, and many others. When the engine includes a variable speed fan, the electronic control unit operates the fan in accordance with received fan request signals. Typically, although variable speed fans have been used with internal combustion engines, the control schemes utilized to control the variable speed fans have been simple and quite conservative to reduce the possibility of accidental overheating and engine component failure.
However, the heavy duty engine business is extremely competitive. Increased demands are being placed on engine manufacturers to design and build engines that provide better engine performance, improved reliability, and greater durability while meeting more stringent emission and noise requirements. Along with all of these, perhaps the greatest customer demand is to provide engines that are more fuel efficient. Demands for fuel efficiency are becoming so great, that all engine driven systems in the vehicle are being scrutinized in attempts to reduce power consumption when possible.
For the foregoing reasons, there is a need for an improved method of controlling an internal combustion engine including a variable speed fan in which the variable speed fan is aggressively controlled to improve vehicle fuel efficiency.
It is, therefore, an object of the present invention to provide a method controlling an internal combustion engine including a variable speed fan in which one or more engine conditions are sensed, and the applied fan request signal is based in part on the measured engine conditions to operate the fan at speeds necessary for cooling, but not excessive, such that overall fuel efficiency is improved.
In carrying out the above object and other objects and features of the present invention, a method of controlling an internal combustion engine is provided. The engine includes a variable speed fan; the variable speed fan is driven in response to an applied fan request signal having a value between a predetermined maximum fan request value and a predetermined minimum fan request value. The engine is operable over an engine speed range between an idle speed and a full speed. The method comprises establishing a fan speed limit, determining an initial fan request signal, and determining the applied fan request signal by limiting the initial fan request signal. The fan speed limit is a maximum allowable fan speed during operation of the engine at all engine speeds in the engine speed range. The initial fan request signal is based on engine operating conditions and has a value between the minimum fan request value and the maximum fan request value.
The maximum fan request value is sufficiently large to cause the fan speed to approach the fan speed limit as the engine speed approaches an intermediate speed between the idle speed and the full speed. The applied fan request signal is determined by limiting the initial fan request signal based on engine speed such that the fan speed approaches the fan speed limit as the engine speed approaches the intermediate speed when the initial fan request signal value is the maximum fan request value. While the initial fan request signal value is the maximum fan request value, the fan speed remains below the fan speed limit as the engine speed approaches the full speed, allowing higher fan speeds at lower engine speeds while avoiding fan overspeed at higher engine speeds.
In a preferred embodiment, the method further comprises monitoring the fan speed, and limiting engine speed, as needed, to prevent the applied fan request signal from causing the fan speed to exceed the fan speed limit. Preferably, determining the initial fan request signal further comprises determining a plurality of preliminary initial fan request signals. Each request signal has a value based on at least one engine condition. The initial fan request signal is determined as the preliminary fan request signal having the greatest value. The above method is suitable for a hydraulically driven variable speed fan wherein hydraulic oil is pumped by a pump to drive a hydraulic fan motor.
Further, in carrying out the invention, a method of controlling an internal combustion engine is provided. The engine includes a hydraulically driven variable speed fan wherein hydraulic oil is pumped by a pump to drive a hydraulic fan motor. The variable speed fan is driven in response to an applied fan request signal having a value between a maximum fan request value and a minimum fan request value. The engine is operable over an engine speed range between an idle speed and a full speed. The method comprises establishing a hydraulic oil threshold temperature, monitoring a temperature of the hydraulic oil, determining an initial fan request signal, and determining the applied fan request signal. The initial fan request signal has a value between the minimum fan request value and the maximum fan request value. The applied fan request signal is determined as the initial fan request signal when the oil temperature falls below the oil threshold temperature. The applied fan request signal is determined as a modified fan request signal having a value greater than the initial fan request signal value to compensate for losses due to increased hydraulic oil temperature when the oil temperature exceeds the oil threshold temperature.
In a preferred embodiment, determining the applied fan request signal further comprises determining a multiplier, and determining the applied fan request signal as a modified fan request signal having a value that is a product of the multiplier and the initial fan request signal value when the oil temperature exceeds the oil threshold temperature. In another embodiment, determining the applied fan request signal further comprises determining an adder, and determining the applied fan request signal as a modified fan request signal having a value that is a sum of the adder and the initial fan request signal value when the oil temperature exceeds the oil threshold temperature.
Still further, in carrying out the present invention, a method of controlling an internal combustion engine is provided. The engine is housed in an engine compartment and includes a hydraulically driven variable speed fan wherein hydraulic oil is pumped by a pump to drive a hydraulic fan motor. The variable speed fan is selectively driven in response to an applied fan request signal based on engine operating conditions. The applied fan request signal has a value between a maximum fan request value and a minimum fan request value. The engine is operable over an engine speed range between an idle speed and a full speed. The method comprises establishing an engine compartment temperature threshold, monitoring a temperature in the engine compartment, and in the presence of the applied fan request signal, driving the hydraulic fan motor with the pump to drive the fan in accordance with the applied fan request signal. In the absence of the applied fan request signal, the method comprises effectively disabling the fan when the temperature falls below the threshold, and otherwise, driving the hydraulic fan motor with the pump to drive the fan at a predetermined speed. The predetermined speed may be a maximum fan speed, or may be a programmable fan speed.
In one embodiment, the pump is a variable displacement pump and effectively disabling the fan further comprises controlling the pump so that there is not any effective pump displacement. In another embodiment, disabling the fan further comprises providing a bypass such that the hydraulic oil that is pumped by the pump bypasses the fan hydraulic motor so that there is not any effective drive to the fan motor. In some embodiments, the engine compartment temperature is an engine compartment air temperature, while in other embodiments, the engine compartment temperature is an intake manifold air temperature.
Even further, in carrying out the present invention, a method of controlling an internal combustion engine in a vehicle having a transmission is provided. The engine includes a variable speed fan and the transmission includes transmission oil. The variable speed fan is driven in response to an applied fan request signal based on engine conditions having a value between the maximum fan request value and the minimum fan request value. The engine is operable over an engine speed range between an idle speed and a full speed. The method comprises establishing a transmission oil threshold temperature for the transmission oil, monitoring a temperature of the transmission oil, and determining a plurality of preliminary initial fan request signals. Each request signal has a value based on at least one engine condition. The transmission oil initial fan request signal is based on the transmission oil temperature and the threshold temperature. The method further comprises determining the applied fan request signal as the initial fan request signal with the greatest value. In a suitable application, the transmission oil temperature is monitored at the transmission oil sump.
Yet further, in carrying out the invention, a method of controlling an internal combustion engine in a vehicle having an air-conditioning system is provided. The engine includes a variable speed fan and the air-conditioning system includes a condenser for transferring heat from a refrigerant during operation. A method comprises establishing a condenser threshold pressure, monitoring a pressure in the condenser, and determining a plurality of preliminary initial fan request signals. Each request signal has a value based on at least one engine condition. A condenser initial fan request signal is based on the condenser pressure and the threshold pressure. The method further comprises determining the applied fan request signal as the initial fan request signal with the greatest value. Of course, it is appreciated that the relationship between condenser pressure and the associated fan request may vary depending on the refrigerant used. Further, the condenser pressure fan request is preferably programmable to allow the fan to operate at a programmed fan speed when condenser pressure is excessive.
The advantages associated with embodiments of the present invention are numerous. For example, in embodiments of the present invention, a variable speed cooling fan is aggressively controlled using one or more of the above methods so that the fan is run at a fan speed that is sufficient to provide adequate engine cooling but the fan is controlled to avoid fuel inefficiencies associated with more conservative fan control strategies of the prior art. In accordance with the present invention, various control techniques may be used alone or together to effectively control the variable speed cooling fan and internal combustion engine to provide fuel efficient operation. Further, in accordance with the present invention, computer readable storage media are provided. A medium of the present invention has instructions stored thereon that are executable by a controller to perform a method of controlling an internal combustion engine in accordance with the control strategies described herein.